The present invention relates to a nuclear magnetic resonance analyzing apparatus; and, more particularly, the invention relates to a magnet device for generating a uniform magnetic field.
Rapid progress has recently been made in the field of organic analysis using nuclear magnetic resonance. In particular, atomic structures of organic compounds, such as proteins, can now be efficiently analyzed by the combined use of nuclear magnetic resonance and superconducting ferromagnetic technology.
An object of the present invention is to provide an NMR spectrometer which is necessary for analyzing atomic structures and interactions of protein molecules in a solution (the solution is prepared by dissolving minute amounts of proteins into a liquid). The NMR spectrometer of the present invention is a special energy spectrometer, which is different from a medical MRI diagnosing apparatus having an image resolution in the order of a millimeter, of the type used for human tomography. Such a special energy spectrometer must have a magnetic field intensity which is higher than that of the typical medical MRI diagnosing apparatus by one digit, a magnetic field uniformity which is higher than that of the medical MRI diagnosing apparatus by four digits, and a stability which is higher than that of the typical medical typical MRI diagnosing apparatus by three digits; and, the design engineering and manufacturing technology thereof are totally different from those of the typical medical MRI diagnosing apparatus.
Details of the conventional high-resolution nuclear magnetic resonance analyzing apparatuses can be found in “NMR of Proteins”, which was written by Yohji Arata and published by Kyoritsu Shuppan in 1996. Recent publications relating to typical equipment components to be utilized for applying NMR to protein analysis include: Japanese Patent Laid-open No. 2000-147082, which discloses a development relating to a superconducting magnet, i.e., multilayer air-core solenoid coils; U.S. Pat. No. 6,121,776, which discloses a birdcage superconducting detection coil; Japanese Patent laid-open Nos. 2000-266830 and 6-237912, each of which discloses a signal detection technique using a conventional saddle-like coil or a birdcage coil; and so forth.
According to the above-listed publications, all of the conventional high sensitivity nuclear magnetic resonance analyzing apparatuses for protein analysis include a superconducting magnet device which uses solenoid coils that are combined so as to generate a magnetic field in a vertical direction, thereby irradiating a sample with an electromagnetic wave of 400 to 900 MHz so as to detect a resonance waveform produced from the sample by the use of a saddle-like or birdcage detection coil. In some cases, the S/N parameter is improved by the use of a detector which is cooled to a low temperature in order to reduce the thermal noise in the detection of signals, as disclosed in the above-mentioned United States Patent.
In the past, the sensitivity of high sensitivity nuclear magnetic resonance apparatuses has been improved through the use of methods of improving the intensity at the center portion of the magnetic field of the superconducting magnet, without changing the basic system structure of the apparatus, including an antenna, a magnet, and so forth. Therefore, although the maximum NMR detection sensitivity, which has heretofore been reported, was achieved by an NMR apparatus of 900 MHz, which uses a large superconducting magnet, such as shown in of FIG. 8, having a center magnetic field intensity of 21.1 Tesla, the basic structure of the NMR apparatus is not any different from that disclosed in Japanese Patent Laid-open No. 2000-147082. For better understanding of the basic structure, a sectional perspective view of the superconducting coils of the NMR apparatus is shown in FIG. 9, wherein a virtual central axis is indicated. In protein analysis using a solution, an increase in the intensity at the magnetic field center has the effects of improving the sensitivity and clarifying the separation of a chemical shift.
The sensitivity improving effects, which depend on the shapes of the detection coils, are mentioned on page 326 of “Book of NMR”, which was written by Yohji Arata and published by Maruzen in 2000, where the solenoid coil is indicated as being advantageous as compared with the saddle-like coil or the birdcage coil in various aspects, as described below.
For example, the solenoid coil is superior in controllability of impedance, filling factor, and RF magnetic field efficiency. According to the “Book of NMR”, however, it is actually impossible to wind solenoid coils around a sample tube which is placed perpendicularly with respect to the magnetic field in the conventional superconducting magnet structure; and, in general, the solenoid coil has not been used in cases where the sensitivity is crucial, such as a case of determining a minute amount of protein dissolved in a solution. For a particularly exceptional case wherein the solenoid coil is used for determining a minute amount of sample solution with high sensitivity, a method which employs a specially designed micro sample tube and a probe combined with the solenoid coil is known.
As a particular example, a method wherein a high-temperature superconducting bulk magnet is magnetized in the horizontal direction, so as to detect NMR signals using a solenoid coil, is disclosed in Japanese Patent Laid-open No. 11-248810. Japanese Patent Laid-open No. 7-240310 discloses the structures of a superconducting magnet and a cooling container that are suitably used for a typical NMR apparatus for eliminating a restriction in the height of the apparatus. However, a method of achieving the detection sensitivity which is required for analyzing proteins, and techniques for controlling the uniformity and the time stability of a magnetic field, have not yet been proposed.